Metal-oxide semiconductor field-effect transistors (“MOSFETs”) are a common type of power switching device. A MOSFET device includes a source region, a drain region, a channel region extending between the source and drain regions, and a gate structure provided adjacent to the channel region. The gate structure includes a conductive gate electrode layer disposed adjacent to and separated from the channel region by a thin dielectric layer.
When a MOSFET device is in the on state, a voltage is applied to the gate structure to form a conduction channel region between the source and drain regions, which allows current to flow through the device. In the off state, any voltage applied to the gate structure is sufficiently low so that a conduction channel does not form, and thus current flow does not occur. In the off state, the device may support a high voltage between the source region and the drain region.
Two major parameters affect the high-voltage MOSFET switch market: break down voltage (BVdss) and on-state resistance (Rdson). Breakdown voltage is the voltage at which the reverse-biased body-drift diode breaks down and significant current starts to flow between the source and drain while the gate and source are shorted together. The on-state resistance is the sum of various resistances, which may include (but are not limited to) one or more of: source diffusion resistance, channel resistance, accumulation resistance, drift region resistance, and substrate resistance. For a specific application, a minimum breakdown voltage is usually required, and designers meet the breakdown voltage requirement at the expense of on-state resistance. This trade-off in performance is a major design challenge for manufacturers and users of high-voltage power-switching devices.
Recently, superjunction devices have gained in popularity to improve the trade-off between breakdown voltage and on-state resistance. However, significant challenges still exist in manufacturing the superjunction devices. Specifically, providing a fast reverse recovery and a small forward voltage for a given forward current, while at the same time preventing degradation of other electrical parameters, without introducing complexity and cost remains a challenge.